A Study of Oral LOXO-292 (Selpercatinib) in Pediatric Participants With Advanced Solid or Primary Central Nervous System (CNS) Tumors

Inclusion Criteria: * Advanced or metastatic solid or primary CNS tumor which has failed standard of care therapies * Evidence of an activating RET gene alteration in the tumor and/or blood * Measurable or non-measurable disease * Karnofsky (participants 16 years and older) or Lansky (participants younger than 16) performance score of at least 50 * Participant with primary CNS tumors or cerebral metastases must be neurologically stable for 7 days prior and must not have required increasing doses of steroids within the last 7 days * Adequate hematologic, hepatic and renal function. * Ability to receive study drug therapy orally or via gastric access * Willingness of men and women of reproductive potential to observe conventional and effective birth control Exclusion Criteria: * Major surgery within two weeks prior to planned start of LOXO-292 * Clinically significant, uncontrolled cardiac, cardiovascular disease or history of myocardial infarction within 6 months prior to planned start of LOXO-292 * Active uncontrolled systemic bacterial, viral, fungal or parasitic infection * Clinically significant active malabsorption syndrome * Pregnancy or lactation * Uncontrolled symptomatic hyperthyroidism or hypothyroidism (i.e. the participant required a modification to current thyroid medication in the 7 days before start of LOXO-292) * Uncontrolled symptomatic hypercalcemia or hypocalcemia * Known hypersensitivity to any of the components of the investigational agent, LOXO-292 or Ora-Sweet® SF and OraPlus®, for participants who will receive LOXO-292 suspension * Prior treatment with a selective RET inhibitor(s) (including investigational selective RET inhibitor\[s\])